EQUISETACE^. 81 



zamites, calamites, equiseta, and ferns. The equiseta are very 

 commonly met with in a vertical position. " It is clear," 

 observes Lyell, " that they grew in the places where they are now 

 buried in strata of hardened sand and mud. I found them main- 

 taining their erect attitude, at points many miles apart, in beds 

 both above and between the seams of coal." We have, I think, 

 ample proof of the existence of Equisetacese in the Carboniferous 

 measures, in the Upper Trias and the Oolite. I think, therefore, 

 that I have said enough in support of my claim to antiquity of 

 type on behalf of the Horsetails. 



Observations on antiquity of type naturally lead to remarks on 

 permanency of type, a subject which, it seems to me, must strike 

 every observer of vegetable life more or less forcibly. Plants 

 constitutionally strong, like Horsetails, with something like armour 

 plating for their protection, and possessing more than one mode of 

 increasing their numbers, were admirably adapted to struggle 

 against the many vicissitudes of climate and other trying condi- 

 tions to which the early flora must have been subjected during the 

 countless ages which have elapsed since the coal-measures were 

 formed. The Glacial period, which must have sorely tried some 

 of the strong and destroyed many of the weakly-constituted 

 plants, seems to have worked little, if any, destruction upon Equi- 

 setaceous plants. They seem to stand in the foreground of 

 witnesses to the doctrine of permanency of type. But they are 

 not the only witnesses. 



I must crave your attention for a few minutes longer, whilst I 



refer to some remarkable observations which have been made by 



Dr. Schweinfurth in the valley of the Nile. They are none the 



less worthy of consideration because they refer to what, for want 



of a better name, I v.-ill venture to designate the historic period. 



The president of the Einnfean Society, Mr. W. Carruthers, F.R.S., 



in his address to the biological section of the British Association, 



at their meeting held at Birmingham in 1886, after referring to 



the result of an examination of certain gravel-beds in the north of 



Eondon, which contained stems and leaves of Clematis vitalba, E., 



willow and birch, the foliage and fruit of Corylus Avella/m, E., and 



Alnus ghifinosa, E., and the rhizomes of Osmiinda regalis, E. — 



" none of which," as he remarked, " could be distinguished from 



New .Series, Vol. I. 



18S8. G 



